How to solder a wire to a battery: the necessary tools and workflow. Ultra-budget spot welding of lithium batteries at home How to solder batteries
When working with mobile home devices or a special tool with a built-in power source, it is often necessary to solder a wire to the battery.
Before embarking on this seemingly simple procedure, you should carefully prepare, which guarantees a reliable and high-quality connection at the end of the work.
Both the alkaline or lithium battery itself and the connecting conductor soldered to it need preparation.
These procedures also include the preparation of the necessary consumables, including such important components as solder, rosin and flux mixture.
The most difficult and crucial moment of the upcoming work is the stripping of the battery terminal, to which it is supposed to solder the connecting wire. This procedure may seem simple only to those who have never tried to do this.
The problem in this case is that the aluminum contacts of the power supplies (finger or other type - it does not matter) are subject to oxidation and are constantly covered with plaque that interferes with soldering.
For their stripping and subsequent isolation from the air, you will need:
- sandpaper;
- medical scalpel or well-honed knife;
- fusible solder and flux neutral additive;
- not very "powerful" soldering iron (no more than 25 watts).
After all these components are prepared, it is necessary to perform the following operations. Firstly, you need to carefully clean the place of the intended soldering, using first a scalpel or knife, and then a fine emery cloth (it will provide a better removal of the oxide film from the contact area).
In parallel with this, the bare part of the soldered wire should be subjected to the same stripping.
Immediately after preparation, you should proceed to the protective treatment of the terminals of a finger-type or any other battery.
Flux processing
To prevent subsequent oxidation of the contact, the battery surface cleaned of plaque should be immediately treated with a flux mixture made on the basis of ordinary rosin.
If, for example, there are no greasy stains from oils on the contacts of the phone’s battery, just wipe them with a soft flannel soaked in ammonia.
After that, it will be necessary, after warming up the soldering iron well, to solder the contact zone with a few quick touches. On this preparation for soldering can be considered complete.
soldering process
After each of the connected parts is cleaned and processed with flux, they proceed to the direct soldering of the wire with the contact area of the battery.
For this final procedure, you can use the same 25-watt soldering iron that was used to prepare the battery terminals from NI or CD.
As a solder, you should choose a fusible composition, and for its good spreading, use a rosin-based flux.
The final soldering procedure should take no more than 3 seconds. This applies to any type of batteries (both NI and CD).
The most important thing is to prevent overheating of the terminal part of the element, as a result of which it can be thoroughly damaged. The possibility of its complete destruction (rupture) during the soldering process is not excluded.
When considering how to solder a wire and a battery, it should be noted that this situation is much more common than it seems. First of all, this concerns a special construction tool (if necessary, soldering screwdriver batteries, for example).
It is not uncommon for the built-in power supply of the tool used to be completely destroyed for some reason, and there is nothing to replace this screwdriver with. In this situation, the conductors feeding the device are soldered to a spare battery designed for the same voltage.
The considered technique can be used when you just need to solder two batteries together.
It should be noted that instead of soldering in production, spot welding is used for batteries. But not everyone has an apparatus for this type of connection, while a soldering iron is a more common device. Therefore, at home, soldering comes to the rescue.
Batteries and accumulators
When powering radio equipment from batteries and accumulators, it is useful to know the common schemes for connecting batteries and accumulators. The fact is that each type of battery has a permissible discharge current.
Discharge current - the most optimal value of the current that is consumed from the battery. If you consume a current from a battery that exceeds the discharge current, then this battery will not last for a long time, it will not be able to fully give up its rated power.
You probably noticed that for electromechanical watches, “finger” (AA format) or “little finger” (AAA format) batteries are used, and for a portable lamp lamp, larger batteries (format R14 or R20), which are capable of delivering significant current and have a large capacitance. Battery size matters!
Sometimes it is necessary to provide battery power to an instrument that draws significant current, but standard batteries (for example, R20, R14) cannot provide the required current, it is higher than the discharge current for them. What to do in this case?
The answer is simple!
It is necessary to take several batteries of the same type and connect them to the battery.
So, for example, if it is necessary to provide a significant current for the device, a parallel connection of batteries is used. In this case, the total voltage of the composite battery will be equal to the voltage of one battery, and the discharge current will be as many times greater than the number of batteries used.
The figure shows a composite battery of three 1.5 volt batteries G1, G2, G3. If we take into account that the average value of the discharge current for 1 AA battery is 7-7.5 mA (with a load resistance of 200 Ohms), then the discharge current of the composite battery will be 3 * 7.5 = 22.5 mA. So, you have to take the quantity.
It happens that it is necessary to provide a voltage of 4.5 - 6 volts using 1.5 volt batteries. In this case, you need to connect the batteries in series, as in the figure.
The discharge current of such a composite battery will be the value for one cell, and the total voltage will be equal to the sum of the voltages of the three batteries. For three elements of the AA format (“finger-type”), the discharge current will be 7-7.5 mA (with a load resistance of 200 Ohms), and the total voltage will be 4.5 Volts.
When it comes to converting a 18650 battery (for a Ni-Cd/Ni-MH screwdriver or household emergency DIY power at home like the Tesla Powerwall), many manuals and instructions are silent about how to connect the batteries. Not all of them are suitable for durability and even safety.
Can 18650 batteries be soldered?
When assembling several cells for a laptop or as part of a large battery (for various purposes of ensuring autonomy up to vehicles), the task is to connect 18650 batteries. And many DIY enthusiasts consider soldering as one of the options.
Remember, lithium-ion batteries (18650 and any other Li-Ion) when heated from a soldering station (and even a low-power soldering iron) are destroyed in their structure and irretrievably lose part of their capacity!
I.e solder 18650 batteries should not be done unless absolutely necessary. Or you will have to put up with a change in the chemical composition and deterioration in performance. In addition, the junction by soldering is unreliable in case of overheating of the battery. Metol is also impractical for compact assembly due to random solder shapes and vulnerability to external influences.
The installers themselves in the comments rightly point out that when exposed to temperature on a lithium-ion battery, you also risk deformation safety valve. This 18650 battery's key safety element is located under the positive terminal and is made from a polymer that withstands maximum operating temperatures. max 120°C.
What do professionals use to properly connect 18650?
To achieve reliability and safety in assembling a battery from several batteries, you can use professional methods or at least those that have proven their practicality and safety.
How to connect 18650 batteries correctly:
contact welding (spot);
using factory holders (holders);
neodymium magnets (powerful perpetual magnets);
gluing;
liquid plastic.
Professionals use the spot welding method - this method is also recommended for industrial assembly of products with 18650 batteries. An example of budget spot welding for the home was examined in detail not so long ago on Geektimes.
Rare-earth neodymium alloy magnets are popular in the DIY community as they hold contacts tightly and allow quick construction of temporary or small household items. For long-term and compact projects, liquid plastic or even glue is best.
To quickly assemble a configuration of several 18650 batteries, you can buy holders with a plastic case and factory contacts for manual soldering without fear of overheating of lithium-ion batteries.
Only in some cases, when other options are not suitable, or impractical (depending on the conditions), should soldering be done by professionals. The choice of low-temperature solder falls on their responsibility, as well as a guarantee of the performance and safety of the battery during further operation.
In the life of every "radio destroyer" there comes a moment when you need to weld several lithium batteries together - either when repairing a laptop battery that has died of age, or when assembling power for another craft. Soldering "lithium" with a 60-watt soldering iron is inconvenient and scary - you overheat a little - and you have a smoke grenade in your hands, which is useless to extinguish with water.
Collective experience offers two options - either go to the trash in search of an old microwave, rip it apart and get a transformer, or spend a lot of money.
I didn’t want to look for a transformer for the sake of several weldings a year, saw it and rewind it. I wanted to find an ultra-cheap and ultra-simple way to weld batteries with electric current.
A powerful low-voltage DC source available to everyone is a common used one. battery from the car. I'm willing to bet that you already have it somewhere in the pantry or you can find it with a neighbor.
I suggest - the best way to get an old battery for free is
wait for frost. Approach the poor fellow, whose car won’t start - he will soon run to the store for a new fresh battery, and he will give you the old one just like that. In the cold, the old lead battery may not work well, but after charging at home in the warmth, it will reach its full capacity.
To weld batteries with current from the battery, we will need to give out current in short pulses in a matter of milliseconds - otherwise we will get not welding, but burning holes in the metal. The cheapest and most affordable way to switch the current of a 12-volt battery is an electromechanical relay (solenoid).
The problem is that conventional 12 volt automotive relays are rated for a maximum of 100 amps, and short-circuit currents during welding are many times greater. There is a risk that the relay armature will simply be welded. And then in the open spaces of Aliexpress, I came across motorcycle starter relays. I thought that if these relays withstand the starter current, and many thousands of times, then it will do for my purposes. This video finally convinced me, where the author tests a similar relay:
My relay was bought for 253 rubles and arrived in Moscow in less than 20 days. Relay characteristics from the seller's website:
- Designed for motorcycles with a 110 or 125 cc engine
- Rated current - 100 amps for up to 30 seconds
- Winding excitation current - 3 amperes
- Designed for 50 thousand cycles
- Weight - 156 grams
The unit pleased with the quality - two copper-plated threaded connections are brought out under the contacts, all wires are filled with a compound for water tightness.
Hastily assembled a "test bench", closed the relay contacts manually. The wire used was single-core, with a cross section of 4 squares, the stripped tips were fixed with a terminal block. For safety, I supplied one of the terminals to the battery with a “safety loop” - if the relay anchor decided to burn and cause a short circuit, I would have managed to pull the terminal from the battery for this rope:
Tests have shown that the machine works on a solid top five. The armature knocks very loudly, and the electrodes give clear flashes; the relay does not burn. In order not to waste a nickel strip and not to practice on dangerous lithium, he tormented the blade of a clerical knife. In the photo you can see a few high quality dots and a few overexposed ones:
Overexposed dots are also visible on the underside of the blade:
At first I piled up a simple circuit on a powerful transistor, but quickly remembered that the solenoid in the relay wants to eat as much as 3 amperes. I rummaged in a drawer and found a MOSFET IRF3205 transistor instead and sketched a simple circuit with it:
The circuit is quite simple - in fact, a MOSFET, two resistors - 1K and 10K, and a diode that protects the circuit from the current induced by the solenoid when the relay is de-energized.
First, we try the circuit on the foil (with joyful clicks it burns holes through several layers), then we take out a nickel tape from the gas holder to connect the battery assemblies. We briefly press the button, we get a loud flash, and we examine the burnt hole. Notepad also got it - it burned not only nickel, but also a couple of sheets under it :)
Even a tape welded with two points cannot be separated by hand.
Obviously, the scheme works, it's up to fine-tuning "exposure and exposure." If you believe the experiments with the oscilloscope of the same friend from YouTube, from whom I spied the idea from the starter relay, then it takes about 21ms to break the armature - from this time we will dance.
YouTube user AvE tests starter relay firing rate against SSR Fotek on an oscilloscope
We supplement the scheme - instead of manually pressing the button, we entrust the counting of milliseconds to Arduina. We will need:
- Arduino itself - Nano, ProMini or Pro Micro will do,
- Sharp PC817 optocoupler with 220Ω current limiting resistor - to galvanically decouple Arduino and relay,
- Step down module like XM1584 to turn the 12 volts from the battery into arduino safe 5 volts
- we also need 1K and 10K resistors, a 10K potentiometer, some kind of diode and any buzzer.
- And finally, we will need nickel tape, which is used to weld batteries.
We fill in the Arduino simple code:
Const int buttonPin = 11; // Shutter button const int ledPin = 12; // Pin with signal LED const int triggerPin = 10; // MOSFET with relay const int buzzerPin = 9; // Buzzer const int analogPin = A3; // Variable 10K resistor to set the pulse length // Declaring variables: int WeldingNow = LOW; int buttonState; int lastButtonState = LOW; unsigned long lastDebounceTime = 0; unsigned long debounceDelay = 50; // minimum time in ms to wait before triggering. Made to prevent false positives when the contacts of the release button bounce int sensorValue = 0; // read the value set on the potentiometer into this variable... int weldingTime = 0; // ...and set the delay based on it void setup() ( pinMode(analogPin, INPUT); pinMode(buttonPin, INPUT); pinMode(ledPin, OUTPUT); pinMode(triggerPin, OUTPUT); pinMode(buzzerPin, OUTPUT) ; digitalWrite(ledPin, LOW); digitalWrite(triggerPin, LOW); digitalWrite(buzzerPin, LOW); Serial.begin(9600); ) void loop() ( sensorValue = analogRead(analogPin); // read the value set on the potentiometer weldingTime = map(sensorValue, 0, 1023, 15, 255); // cast it to milliseconds between 15 and 255 Serial.print("Analog pot reads = "); Serial.print(sensorValue); Serial.print( "\t so we will weld for = "); Serial.print(weldingTime); Serial.println("ms. "); // To prevent false positives of the button, first make sure it is pressed for at least 50ms before starting welding: int reading = digitalRead(buttonPin); if (reading != lastButtonState) ( lastDebounceTime = millis(); ) if ((millis() - lastDebounceTime) > debounceDelay) ( if (reading != buttonState) ( buttonState = reading; if (buttonState == HIGH) ( WeldingNow = !WeldingNow; ) ) ) // If command received, then start: if (WeldingNow == HIGH) ( Serial. println("== Welding starts now! =="); delay (1000); // Give three short beeps and one long beep to the speaker: int cnt = 1; while (cnt<= 3) {
playTone(1915, 150); // другие ноты на выбор: 1915, 1700, 1519, 1432, 1275, 1136, 1014, 956
delay(500);
cnt++;
}
playTone(956, 300);
delay(1);
// И сразу после последнего писка приоткрываем MOSFET на нужное количество миллисекунд:
digitalWrite(ledPin, HIGH);
digitalWrite(triggerPin, HIGH);
delay(weldingTime);
digitalWrite(triggerPin, LOW);
digitalWrite(ledPin, LOW);
Serial.println("== Welding ended! ==");
delay(1000);
// И всё по-новой:
WeldingNow = LOW;
} else {
digitalWrite(ledPin, LOW);
digitalWrite(triggerPin, LOW);
digitalWrite(buzzerPin, LOW);
}
lastButtonState = reading;
}
// В эту функцию вынесен код, обслуживающий пищалку:
void playTone(int tone, int duration) {
digitalWrite(ledPin, HIGH);
for (long i = 0; i < duration * 1000L; i += tone * 2) {
digitalWrite(buzzerPin, HIGH);
delayMicroseconds(tone);
digitalWrite(buzzerPin, LOW);
delayMicroseconds(tone);
}
digitalWrite(ledPin, LOW);
}
Then we connect to the Arduino using the Serial monitor and turn the potentiometer to set the length of the welding pulse. I empirically picked up a length of 25 milliseconds, but in your case the delay may be different.
By pressing the release button, the Arduino will squeak several times, after which it will turn on the relay for a moment. You will need to lime a small amount of tape before you select the optimal pulse length - so that it welds and does not burn holes through.
As a result, we have a simple unsophisticated welding installation, which is easy to disassemble:
A few important words about safety:
- When welding, microscopic spatter of metal can scatter to the sides. Don't show off, wear goggles, they cost three kopecks.
- Despite the power, the relay can theoretically “burn out” - the relay armature will melt to the contact point and will not be able to return back. You will get a short circuit and a quick warm-up of the wires. Think in advance how you will pull off the terminal from the battery in such a situation.
- You can get different degrees of welding depending on the battery charge. To avoid surprises, set the welding pulse length on a fully charged battery.
- Think in advance what you will do if you make a hole in the 18650 lithium battery - how will you grab the hot element and where will you throw it to burn out. Most likely, this will not happen to you, but with video consequences of spontaneous combustion of 18650 better familiarize yourself in advance. At a minimum, prepare a metal bucket with a lid.
- Control the charge of your car battery, do not allow it to be strongly discharged (below 11 volts). This is not useful for the battery, and don’t help out a neighbor who urgently needs to “light up” a car in winter.